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[untitled]

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00:31:00

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mpeg2video

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San Francisco 13, The City 3, Us 3, San Andreas 3, Haward 2, Marina 2, Kobe 2, Mexico City 2, Valencia 2, California 2, Excellerateom Ters 1, Lori Johnson 1, Shakesing 1, G. You 1, John Paxton 1, Harvey 1, Southern California 1, Westportal 1, Mississippi 1, The Dolores 1,
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  SFGTV2    [untitled]  

    August 26, 2013
    6:30 - 7:01am PDT  

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>> hello and welcome to the department and building inspection lunch program. we are talking today about earthquakes and we are going to talk about the issues that make us particularly vulnerable in san francisco and talk about the policy issues and do earthquake response and hopefully in our earthquake recovery. pat, who is a structural engineer and a guy that has looked at earthquake building upgrades in san francisco, yeah.
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than anybody and he has his earthquake dog harvey. >> okay. that's enough. and john paxton who is a part of caps and it's a community action plan for seismic safety and sponsored by the department of building. and what are the significant impacts of earthquake and how can we mitigate that to meet the goals we want to make. one of the things we want to talk about are, what are your reasonable expectations? people have different goals about what they expect. a lot of people say, i live in a house, the city wouldn't let me live in a house that wasn't
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safe, would they? i live in a brand-new house and it's absolutely fine. those are unreasonable expectations and why they are. there's, for example. nothing that the earthquake proof. that's always stuff inside that is damaged and life line connections, telephone and water that make habitability a problem. san francisco's earthquake hazard has a whole over lay of problems. first is our location. by the 2 faults. the san andreas, which is off shore of san francisco, and is
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about how far off shore? maybe a mile. so it's very, very close to the city and runs up to marin, >> a million years of earthquake movement created. that used to be in southern california. it's an active fault and the other is the hay ward fault. geology and other people say this is a fault that is more likely to have slippage. and the hay ward fault runs through the university of california >> right through memorial stadium, i understand. >> it's one site moving relative to the other >> and downtown san francisco,
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the heart of san francisco, this is basically almost exactly between the hay ward faults and san andreas. >> although if you live in the richmond district and the hay ward fault goes off, you won't feel the earthquake. you won't be able to stand. >> so what you're saying is the closer you are. >> that's why it's good to be in the middle. if you are on one extreme and the fault goes off, the shaking will be pronounced >> how many people were in san francisco in 89?
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anyone in the marina in 89? >> if you were in the main portion, the ground excelleration was 90 percent. if you way 100 pounds, the pound moved with 9 pounds. if the hay ward fault goes off, most of san francisco will feel 20 to 25 percent, the marina which will shake 30 percent. so if the hay ward fault goes off, san francisco will shake 3 or 4 times harder than in 89 and twice as long. >> the haward fault has return
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cycles plus or minus 10 for the last 140 years. the last was 1868. we are 140 years since the last haward fault went off. so, i would say, it's pretty likely it won't slip within the next 10 years. that will give you ground shakesing 3 to 4 times as last time. >> we have, pat and i and i couple of other people have run a program how to prepare in your life and home with problems related to an earthquake. that's not what our discussion is today. it's more of a global policy issues. one is proximity to the fault. how certain are geo technical
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engineering that the actual proximity of the fault is in fact going to affect how strong the ground motion is? does a mile make a difference? >> it came out in kobe earthquake. >> i was actually there. >> the roof came off. it was hard to stand up. i was 6, 7 miles away. in the city, people couldn't stand up. >> they determined using excellerateom ters. you will have near field effect, the easy way to explain it, if you were standing next
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to a rail road track. the train makes sound and generates and the sound waves tumble. the same thing happens with an earthquake. those /tkpwraupbd waves tumble upon themselves and increase the intensity of the shaking. it's called near field effect. we probably won't get that on the haward fault, but on the san andreas fault. they will have very pronounced shaking. we will also have more interaction because of poor soils that interact with earthquake waves. you can have a moderately
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distant waves and it will be higher in the bay area and people don't realize how much of the city has been filled. there's a tremendous amount filled in and in those areas, the ground will shake dramatically harder. there's a lot of interaction that plays into the interaction of the intensity. >> this map was adopted by the state of california after its study of the areas that are potentially liquifiable. they are wet areas or fill areas that amplify the earthquake forces >> you can actually have the ground turn to liquid like quick sand. >> if you look at the map, there are green areas and blue
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areas, just so you can understand, the blue areas are potential landslide areas. that's a different issue. but we do have potential landslide areas. all the green areas are potentially liquifiable. if pat says, you are going to have.9 g. you could have substantial amp liification of this. this fascinating old map from the 1800's. it shows what san francisco looked like before a lot of it was filled. this is the mission district, the marsh of mission bay went all the way up to 7th and mission. that's how big the marsh is.
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the bay went up to montgomery street. so all this is bay. all this is bay. all this is bay. do you see these city streets out here? this is a small section of the city. this has all been filled. >> if you look at this map was recently adopted by the state, as their hazhard map. that's what these green areas are. just enormous mission area. >> this is an interesting tid bit. most people don't realize. there was a creek that flowed out of a lake in the mission. the lake was three city blocks large. it was at 17th and valencia. there's a plaque out there. you could sail a boat up the
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creek that flowed out into the bay into the lake at 7 the and mission and go sailing. it was that big. that land was so valuable because everybody wanted to live east of twin peaks because the weather was better here. warm. they filled in as much land as they probably could. and then they were forceed to building on the other side of twin peaks. where the weather wasn't as nice. >> i live in inner sunset. in 1906. in the big earthquake, that area had dramatic effect. one building settled down into the lake bed. >> the largest loss of life was at 17th and valencia hotel.
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the fire department came in, drown the people in the basement and the fire came and killed a bunch more people. across the street, there was a 3 story building any after the earthquake, the first floor went straight down. didn't crush. just liquified and created 1 story basement. >> we have unusual soil conditions and then, on top of that, we have built environment. we have buildings built of all different kinds of construction types and dates. when you put those together. maybe you are sitting on rock areas that are built solidly that will have little impact
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and you have other buildings, soft story buildings and people have essentially the same expectation. >> and the building department would come knock on my door and tell me it wasn't safe >> there are very few retrofitted laws. you have to make brick buildings saver. >> you have to reduce the risk of life lost. >> so the brick building standard is a low standard. it was to prevent catastrophic collapse. the brick buildings, we have 1800 of them.
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most have been upgraded to prevent catastrophic deaths. it's the lowest possible >> and they might need to be torn john. by the way, this was lori johnson. this is our risk analysis and has done work to reconstruction especiallily in kobe and post katrina. >> thanks for joining us >> you are going to be coming to the caps meeting. >> i am on the advisory committee. >> most of san francisco of densely built and not very tall. >> what is the relationship of hazard between large buildings and the typical san francisco low rise? >> most large buildings are
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structural steel buildings and they do well in earthquakes. there's a class there were popular in the 50's and 60's, there's a lot of apartment buildings, about 10 or 15 story tall. they are the worst class to be in. those midrise buildings >> how many of those do you think there are? >> about 500 plus or minus 200. >> we have seen how they perform. for example, in mexico city. >> they look like stacks of pan cakes. they built row after row of these concrete buildings and mexico city is built around an island in the middle and a big
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lake and they filled it in, just like san francisco. the floors were stacked like this. it looked like a stack of pan cakes. >> how did this compare older buildings of the 1920's or 30's? >> they will have more reenforcing in them. they had a tendency to use more round columns with spiral hoops. they don't necessarily catastrophicly collapse. in a perverse sense, the 50's and 60's buildings, you don't want to be in. i am in a 1920 building
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>> i wanted to clarify, we have beautiful, very ornate buildings they are taller. a lot of apartment buildings. >> those are mostly steel framed buildings. in the 50's and 60's, they wanted to create open floor spaces and they went to concrete spaces and thought it was great until the san fernando earthquake and the earthquake came and the building disappeared. they said, oops and changed the
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code immediately. >> we look at it and say, it didn't do what we thought. the codes are rarely perspective. how can we make that happen? they wait for a catastrophe and then change it >> just to clarify. we don't have instrumentation to record the shaking and to do a computer simulation is difficult to do without the data. we only learn through events. not all the records we have are indicative of how every earthquake shaking event will
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be like. >> we have recently amended the code to have instruments in them so we can record and how much the earth has moved. that's terrific. not many existing buildings are instrumented. one the things we will look at, at the caps program is to retrofit them. we can look at other after earthquakes. it had similar types of faults we have here. there are a lot of similarities. >> there is something, of the type of construction. there are debate about how they
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will perform. we know how soil conditions will affect. how good your building is, is going to be predominated by soil conditions. if you put 3 engineers in the room, you get 5 opinions. there are buildings that engineers can look at and agree there's not a chance in hell it will survive. there are buildings where there's no reasonable belief, matter of fact, we would be shocked the building would still be standing in an earthquake. >> the after earthquakes that are common and then we have the design earthquakes that we use to think about what is the reasonable earthquake and then
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we have the maximum possible earthquake, like the 1906. >> 500-year retu6-cycle. >> i take it back. most wood frame buildings, probably pre-existed before code >> which was in the early 70's? >> they had requirements in the 50's and 60's. we don't consider building code until 1973. major buildings, was designed by a genious and it was ahead of the time. they required an engineer. smaller buildings, you didn't need an engineer on all of them. >> basically, if your building was built before early 70's. it's likely to have some
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earthquake resistance and resilience of the cost of construction. it wasn't specifically designed to with with stand and earthquake. >> most of the sun stream homes. these are track homes, mostly built to speck homes. built the way they always built. they have a degree of earthquake resistance. >> they have a tendency to pound together and the buildings in the middle survive because the earthquake isn't long enough. the individual at the end of the block is like the book at the end of shelf. they fall over and the next one falls over. >> in the marina. we saw corner believes collapse. >> there are 2 ways to look at earthquakes. i think each one of us wants to
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know how our house, where we live is going to perform. we also need to look at how the city is going to perform. pat makes a good point, most the newer buildings will perform better. keep in mind, the studies we have done certainly show is that most the vulnerable buildings will be residential. half of the residential units were built before world war ii. we have a very old housing stock. we have the oldest housing stock this side of mississippi. and that's where our problems are most likely to be. >> i going to test the microphone and ask people how you expect your home to perform. >> anybody who wants to share.
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tell us, what kind of building. do you live in a wood frame >> yes >> after a major earthquake. what's your expectation. >> i am afraid from last year's earthquake class, you mentioned. the house might pop to the street because my garage is empty. >> is it in the middle of the block? >> middle. >> there's less chance. sir, what kind of building do you live in? >> i live in an apartment if ground floor parking. >> in the middle of the block, corner.
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>> corner. >> are there openings on both sides? >> yes. on both sides. >> it's a wood framed building? >> it seems to be a hybrid. with concrete and steel and wood frame on top of that. >> we don't often see that. modern buildings have a podium. >> what neighborhood are you in >> dolores park. >> you will hit the lake. if are in the dolores, you are in pretty good shape. >> what is your expectation of what your building is going to be like after a major earthquake? >> i am really not sure. that's my concern. >> i see. this gentlemen is correct. his concern is his building.
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you have to look at it block by block. you can see that the edges of the fill area vary block by block. let me point out in cole valley, there was an old pond and an amusement park with a trolley. that pond was filled in, that's a potential liquify site. so we have to look at the soil. >> there are area that is are fascinating. westportal, there was a creek that flowed all the way down to pig lake. i think that's what the spanish
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called it. there was a deep ravine. they filled it in with the tunnel muck and they filled in the ravine and built houses. the other area is really interesting, down 18th street. there was a creek coming from eureka. there is a street called pond. it's not a coincidence. >> part of what we're going too try to do is update this map and give it historical data. there are more significant data. >> how do you know i

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